1. Field of the Invention
The present invention relates to improvement in or relating to a photoelectric conversion device in which a number of semiconductor elements are sequentially arranged on a substrate in side-by-side relation and connected in series.
The invention also pertains to a method for the manufacture of such a photoelectric conversion device.
2. Description of the Prior Art
A wide variety of photoelectric conversion devices have been proposed which are of the type wherein a number of semiconductor elements are formed side by side on a substrate in a sequential order.
Some of the conventional photoelectric conversion devices employ a plate-like member of glass or ceramics as the substrate; in this case, since the substrate is brittle, much care is necessary in handling the photoelectric conversion devices. Moreover, since the glass or ceramic substrate is inflexible, difficulty is encountered in mounting the photoelectric conversion device on a light receiving panel.
Sometimes the substrate is formed by a plate-like member of synthetic resin or metal; such a substrate is not readily broken and can be made flexible by reducing its thickness.
However, a substrate made of a thin plate-like member of synthetic resin, when pulled, tends to elongate as compared with a substrate formed by a thin plate-like member of metal. This introduces the possibility that elongation of the substrate caused, for example, when mounting the photoelectric conversion device on a light receiving panel, imposes a mechanical strain on the semiconductor elements sufficient to deteriorate their characteristics or break them down, making it impossible for the photoelectric conversion device to attain its required photoelectric conversion efficiency or perform its normal operation.
The substrate of synthetic resin is apt to be degenerated by light which impinges it during irradiation of the photoelectric conversion device. The degeneration of the substrate resulting from long-time service of the photoelectric conversion device often distorts the substrate itself or makes it pervious to air or water. The distortion of the substrate imposes a mechanical strain on the semiconductor elements formed thereon, resulting in degradation of their characteristics, as mentioned above. When the substrate becomes pervious to air or water, water or undesirable components pass through the substrate to reach the semiconductor elements to adversely affect them.
Accordingly, the photoelectric conversion device using a substrate of synthetic resin, when used for a long period of time, may become unable to provide the required photoelectric conversion efficiency or to stand further use.
Furthermore, the substrate of synthetic resin is readily degenerated by heat applied from the outside or generated in the semiconductor elements while in use. This also distorts the substrate or makes it pervious to air or water, cutting down the photoelectric conversion efficiency of the device or putting it out of order.
Besides, the substrate of synthetic resin is lower in heat resistance than the metallic substrate, and hence it is likely to be degenerated or deformed by heat applied for forming the semiconductor elements on the substrate. Accordingly, the use of the substrate of synthetic resin introduces difficulty in the manufacture of the photoelectric conversion device.
When the substrate is formed by a thin plate-like member of metal, there are no such defects as mentioned above. In this case, however, since the substrate surface is conductive, a relatively thick insulating layer must be interposed between the substrate and the semiconductor elements. This impairs the flexibility of the photoelectric conversion device and calls for additional steps of forming the insulating layer on the substrate prior to the formation thereon of the semiconductor elements, thus introducing complexity in the fabrication of the device by that.
There are times when the semiconductor elements on the substrate are each formed of a single-crystal semiconductor laminate member. In such a case, even slight bending of the photoelectric conversion device may impose a strain on the single-crystal semiconductor laminate member to degrade the characteristics of the semiconductor elements, resulting in the photoelectric conversion device becoming poor in its characteristics or being put out of order.
In addition, since the single-crystal semiconductor laminate member is difficult to form at low cost and with ease, its use is not preferable for the fabrication of the photoelectric conversion device.
In some of the conventional photoelectric conversion devices, the semiconductor photo elements are electrically connected in series one after another. In this case, the semiconductor elements are usually connected through the use of electrical connecting means formed by conductive layers or leads provided separately of their electrodes. But the electrical connecting means occupy a significantly large area of the substrate relative to the area occupied by the semiconductor elements on the substrate. In other words, the number of semiconductor elements formed on the substrate per unit area is small and, consequently, the photovoltage per unit area of the substrate is low. Furthermore, the electrical connecting means is required, thus introducing complexity in the manufacture of the photoelectric conversion device.
In the fabrication of the photoelectric conversion device, the semiconductor elements are usually formed by a method including the following steps (a) to (c):
(a) A first conductive layer which will ultimately act as a first electrode of each semiconductor element is formed on the substrate, a first mask of a predetermined pattern is formed (by an ordinary printing method) on the first conductive layer and then the first conductive layer is selectively etched away through the first mask, thereby providing the first electrode of each semiconductor element.
(b) A semiconductor laminate member which will ultimately serve as a semiconductor laminate member of each semiconductor element having formed thereon a PN or PIN junction is formed on the substrate in such a manner that the first electrodes of the semiconductor elements, formed by the step (a), may be buried in the semiconductor laminate member, a second mask of a predetermined pattern is formed on the semiconductor laminate member and then the semiconductor laminate member is selectively etched away through the second mask, thereby providing the semiconductor laminate member of each semiconductor element.
(c) A second conductive layer which will ultimately serve as a second electrode of each semiconductor element is formed on the substrate in such a manner that the semiconductor laminate members of the semiconductor elements, formed by the second step (b), may be buried in the second condutive layers, a third mask of a predetermined pattern is formed on the second conductive layer and then the second conductive layer is selectively etched away through the third mask, thereby providing the second electrode of each semiconductor element.
According to the conventional method including the abovesaid steps (a) to (c), the formation of the many semiconductor elements calls for three etching steps using masks, i.e. the first electrode forming step including the formation of the first mask and the selective etching through using the first mask, the semiconductor laminate member forming step including the formation of the second mask and the selective etching through using the second mask and the second electrode forming step including the formation of the third mask and the selective etching using the third mask. Accordingly, the prior art method has the defect of involving many steps for the manufacture of the photoelectric conversion device.
According to the conventional manufacturing method, the etching masks must be formed accurately in position but the positioning is very difficult, which is a serious obstacle to the fabrication of the photoelectric conversion device.
Furthermore, there is a certain limit to forming the etching masks in predetermined patterns with high precision. This imposes severe limitations on the number of semiconductor elements per unit area of the substrate and consequently the photovoltage per unit area of the substrate.
Moreover, according to the prior art manufacturing method, the semiconductor elements are usually electrically connected in series through the use of electrical connecting means formed by conductive layers or leads provided separately of the first and second electrodes of the semiconductor elements. This also constitutes an obstacle to simplification of the manufacture of the photoelectric conversion device. In addition, the electrically connecting means occupies a significantly large area of the substrate relative to the area occupied by the semiconductor elements. This also imposes severe limitations on the number of semiconductor elements per unit area of the substrate and consequently the photovoltage per unit area of the substrate.